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1 - Influence of magnetic field and ionization on gradient driven instability in an E ⃗×B ⃗ plasma
- Munish Rajat Dhawan Dimple Sharma Hitendra MalikAn E ⃗×B ⃗ plasma is important for various applications including Hall thrusters and magnetic nozzle for long-lasting space propulsion. Such a cross field arrangement in inductively coupled plasma plays vital role in film deposition and etching that are the basic أکثرAn E ⃗×B ⃗ plasma is important for various applications including Hall thrusters and magnetic nozzle for long-lasting space propulsion. Such a cross field arrangement in inductively coupled plasma plays vital role in film deposition and etching that are the basic ingredients in semiconductor industries; though in these applications, only the electrons are magnetized which enhance the plasma production and hence, ultimately control the etching aspect ratio and film quality. In the present work, an E ⃗×B ⃗ plasma is considered where ionization takes place and finite temperature gradient also exists. Specifically, a theoretical model is developed for analysing the effect of magnetic field on the density gradient driven instability. The growth rate of the instability is evaluated as a function of plasma background density, scale length of density gradient, ionization frequency, charge on ions, ion temperature gradient, temperatures of plasma species and magnetic field. To generalize the situation, case of different masses of the ions is also reviewed by considering both the electrons and the ions to be magnetized. تفاصيل المقالة -
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2 - Modified Bohm’s criterion in a collisional electronegative plasma having two-temperature non-extensive electrons
Rajat Dhawan Mayand Malik Hitendra K. MalikPlasma-material interaction has been a subject of interest for the past several decades due to its importance in various fields of research such as film deposition, surface nitriding, plasma etching, plasma reactors at low-pressure conditions etc. During this interactio أکثرPlasma-material interaction has been a subject of interest for the past several decades due to its importance in various fields of research such as film deposition, surface nitriding, plasma etching, plasma reactors at low-pressure conditions etc. During this interaction, the presence of negative ions further plays a vital role to ease defect-free analysis of soft substrates. The response of plasma through the sheath formation, when a metallic plate or probe is inserted into it, depends on the plasma characteristics / parameters and the bias voltage used on the plate or probe. The Bohm’s criterion decides such kind of interaction. The present work theoretically demonstrates a modified Bohm’s criterion in an electronegative plasma which is collisional and has two-temperature non-extensive electrons (hot and cold electrons). The behaviour of positive ions is considered through their fluid equations, whereas the negative ions are taken to follow Boltzmann distribution. While writing the basic equations, ion source term and ionization rate are retained and Sagdeev’s potential approach is employed to evaluate the Bohm’s criterion which reveals a band for the positive ion velocity, means maximum and minimum values for the ion velocity. This modified Bohm’s criterion is studied under the effects of various plasma parameters. تفاصيل المقالة -
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3 - Influence of the hot filament on the electrical breakdown characteristics in the presence of Ar/N2
Arian Fateh Borkhari Kiomars YasserianAbstractThe influence of a hot filament on the electrical breakdown characteristics is studied for different ratios of argon and nitrogen gases for a wide range of pressure. The vacuum tube consists of two parallel plane stainless steels used as cathode and anode accomp أکثرAbstractThe influence of a hot filament on the electrical breakdown characteristics is studied for different ratios of argon and nitrogen gases for a wide range of pressure. The vacuum tube consists of two parallel plane stainless steels used as cathode and anode accompanied with a tungsten filament located behind the cathode. Paschen’s curves are obtained for different ratios of argon and nitrogen as a function of pressure for various electric currents of the hot filament. The first and second Townsend coefficients as well as the ionization efficiency and secondary ionization coefficient are obtained for different filament currents. In addition, the influences of the nitrogen partial pressure on the forgoing parameters are obtained. It is shown that, increase of the filament current causes the decrease of the electrical breakdown voltage which is more pronounced in low pressures. Furthermore, introducing the nitrogen gas leads to the increase of the breakdown voltage and decrease of the ionization efficiency as well as the first and second Townsend coefficients. Moreover, it is concluded that, in the middle range of pressure, the presence of the hot filament results to the electrical breakdown which reveals the linear features. تفاصيل المقالة -
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4 - A method to improve the accuracy of diode in vivo dosimetry for external megavoltage photon beams filtered by wedges
Alireza Mohammadkarim Mahmoud Allahverdi Hasanali Nedaie Mahbod Esfehani Alireza Shirazi Ghazale GerailyAbstractDiode in vivo dosimetry is widely considered to be an important tool for quality improvement of patient care in external radiotherapy. In vivo dose measurements for wedged photon beams require correction factor estimation for difference in wedge angles and field أکثرAbstractDiode in vivo dosimetry is widely considered to be an important tool for quality improvement of patient care in external radiotherapy. In vivo dose measurements for wedged photon beams require correction factor estimation for difference in wedge angles and field sizes. The diode dosimeters that were used in this study were two different models of PTW products; T60010L and T60010M models were used for 60Co and 6-MV photon beams, respectively. The values of off-axis wedge correction factor were determined at two different physical situations in the wedged and non-wedged directions on the entrance surface of the polystyrene phantom. The wedge correction factor at various depths was then estimated by a proposed method. Results show that the absorbed dose at each depth can be estimated by applying accurate wedge correction factor at depth, on entrance surface dose with negligible probable errors (below 1.2%). تفاصيل المقالة -
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5 - Soliton reflection in a magnetized inhomogeneous warm plasma: effect of ionization
Hitendra K. Malik Jyoti Ravinder KumarAbstractThe reflection of nonlinear solitary waves is studied in a plasma under the effect of an external magnetic field and constant ionization along with finite ion temperature. To investigate the reflection of solitary waves, relevant modified Korteweg–deVries equati أکثرAbstractThe reflection of nonlinear solitary waves is studied in a plasma under the effect of an external magnetic field and constant ionization along with finite ion temperature. To investigate the reflection of solitary waves, relevant modified Korteweg–deVries equations for the right and left going waves are derived, and coupled at the point of reflection for obtaining the expression of reflection coefficient. The solitary waves are found to shift after their reflection. Variation of reflection coefficient and shift are studied for different plasma parameters like ion temperature, ionization rate and wave propagation angle or the obliqueness of magnetic field. تفاصيل المقالة -
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6 - Effect of external applied electric field on the silicon solar cell’s thermodynamic efficiency
R. Zieba Falama Justin Mibaile E. Guemene Dountio Noël Djongyang Serge Y. Doka Timoleon C. KofaneAbstractThis paper presents a possible solution to improve the efficiency of photovoltaic solar cells. An external electric field is applied on a silicon photovoltaic solar cell, inducing band-trap ionization of charge carriers. Output current is then monitored and the أکثرAbstractThis paper presents a possible solution to improve the efficiency of photovoltaic solar cells. An external electric field is applied on a silicon photovoltaic solar cell, inducing band-trap ionization of charge carriers. Output current is then monitored and the thermodynamic efficiency is calculated. Results show on the one hand a significant increase in efficiency for a certain margin of applied electric field, and on the another hand the instabilities of efficiency. A simple approach is then suggested for the implementation of these results. An efficiency of 67% has been reached for an applied electric of 1586 V/Cm. تفاصيل المقالة -
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7 - On validity of paraxial theory for super-Gaussian laser beams propagating in a plasma
Lalita Devi Hitendra K. MalikAbstractIn the present paper, we have investigated a situation where a high intensity laser beam passes through a gas and ionizes this gas by tunnel ionization. Here the electric field of the laser provides a sufficient velocity to the electrons to surpass the Coulomb b أکثرAbstractIn the present paper, we have investigated a situation where a high intensity laser beam passes through a gas and ionizes this gas by tunnel ionization. Here the electric field of the laser provides a sufficient velocity to the electrons to surpass the Coulomb barrier of the atom. Owing to the ionization the plasma density enhances which affects the laser beam propagation. The use of paraxial ray approximation theory for the present case of super-Gaussian lasers reveals the self-focusing of the beams and frequency upshifting. The predicted self-focusing of the laser beams is contrary to the expected outcome of defocusing of these beams in the plasma, indicating that the paraxial theory may not be valid for the case of super-Gaussian lasers even for the inclusion of most of the near axis region in the theory. تفاصيل المقالة -
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8 - Investigation of dopant centres dominating the conduction process in the bulk of un-doped GaSb
Megersa Wodajo ShuraAbstractIn this paper, first, the theoretical description of the effects of the dopant densities and the activation energies on the ionization densities, the chemical potentials corresponding to each dopant levels, the majority carrier densities and the Fermi-energy lev أکثرAbstractIn this paper, first, the theoretical description of the effects of the dopant densities and the activation energies on the ionization densities, the chemical potentials corresponding to each dopant levels, the majority carrier densities and the Fermi-energy levels in one-acceptor-level system, highly compensated system and two-acceptor-level system are described in detail. Upon fitting the theoretical to the experimental results obtained by the temperature-dependent Hall effect measurements for three samples of un-doped GaSb, the dopant densities and the activation energies for a system with different dopants are investigated. The obtained results revealed that the dopant activation energy has less (no) effect on the Fermi-energy level and the majority carrier density in the highest temperature regimes. The doping density has also less (no) effect on the Fermi-energy level in the lowest temperature regimes. Finally, fitting of the theoretical to the experimental Hall effect measurements results confirmed the presence of three acceptor and one donor levels dominating the majority carrier densities at different temperature regions in all the samples of un-doped GaSb semiconductor. تفاصيل المقالة -
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9 - Classical DFT Study on Atomic Electronegativity
Mohammad Hossien Ghorbani Reza Fazaeli Arash GhoorehianThe term electronegativity .was introduced by Linus Pauling, who characterized on the basis ofthermodynamic data from the energies of the single bonds. In present study, the Density Functional Theory(DFT) was used to calculate electronegativity of atoms. The base of cal أکثرThe term electronegativity .was introduced by Linus Pauling, who characterized on the basis ofthermodynamic data from the energies of the single bonds. In present study, the Density Functional Theory(DFT) was used to calculate electronegativity of atoms. The base of calculation is similar to Pauling andMulliken methods. The results indicate that the largest value of electronegativity for Fluorine atom and thenplotted the electronegativity values versus to atomic numbers. We have selected scale of electronegativitybase on Pauling's method. Also we presented an empirical formula for electronegativity calculation that thevalue of the electronegativity is a function of number of valence electron, in Addition to ionization potentialand electron affinity. Our novel strategy designed by• Natural Population Analysis (NPA) method. Allcalculations were performed using B3LYP method and aug-cc-pVTZ, 6-31 THEG(2d0, SDDALL andLANL2DZ basis set in Gaussian 03W. تفاصيل المقالة -
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10 - Derivation of ionization energy and electron affinity equations using chemical hardness and absolute electronegativity in isoelectronic series
S. Kaya C. KayaChemical hardness () and absolute electronegativity () have important applications in chemistry. Inthe conceptual Density Functional theory (DFT), these concepts has been associated with electronicenergy and the relationship with ionization energy (I) and electron aff أکثرChemical hardness () and absolute electronegativity () have important applications in chemistry. Inthe conceptual Density Functional theory (DFT), these concepts has been associated with electronicenergy and the relationship with ionization energy (I) and electron affinity (A) of these concepts hasbeen given. In this study, graphical method was used in order to see the relationship with the atomicnumber (Z) of chemical hardness and absolute electronegativity in isoelectronic series. These serieswas considered because all members of an isoelectronic series have the same shielding constant.Chemical hardness and electronegativity equations depending on atomic number were obtained fromgraphs of =f(Z) and =f(Z) for isoelectronic series that contain electron from 1 to 20. Ionizationenergy and electron affinity equations were obtained making use from the chemical hardness andelectronegativity equations. In the last stage, the relationship with the number of electron ofcoefficients in the ionization energy and electron affinity equations was examined. As a result, newequations consistent with experimental results that depending on atomic number and number ofelectron were obtained. تفاصيل المقالة -
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11 - بررسی امکان اندازهگیری ترکیبات فنولی حلقوی در شکر قهوهای به روش DFT
پرستو مسگران کریمی مسعود هنرورمقدمه: گیاه نیشکر و شکر حاصل از آن حاوی انواع ترکیبات فنولی است که خواص آنتی اکسیدانی مطلوبی نیز دارند. از این رو پژوهش حاضر به بررسی امکان اندازه گیری این ترکیبات فنولی در شکر قهوه ای با استفاده از روش DFT می پردازد. مواد و روشها: در این پژوهش از دو نوع شکر پخت (II) أکثرمقدمه: گیاه نیشکر و شکر حاصل از آن حاوی انواع ترکیبات فنولی است که خواص آنتی اکسیدانی مطلوبی نیز دارند. از این رو پژوهش حاضر به بررسی امکان اندازه گیری این ترکیبات فنولی در شکر قهوه ای با استفاده از روش DFT می پردازد. مواد و روشها: در این پژوهش از دو نوع شکر پخت (II) و پخت (III) در فرایند تولید شکر نمونه گیری شد و در ابتدا با استفاده از دستگاه کروماتوگرافی مایع با کارایی بالا (HPLC) نوع و نسبت ترکیبات فنولی حلقوی در دو نوع شکر پخت (II) و پخت (III) شناسایی و تعیین شد. در گام بعدی و برای اولین بار، با استفاده از روش محاسباتی پیشرفته نظریه تابعیت چگالی DFT و براساس محاسبه انتالپی تفکیک پیوند BDE)) و پتانسیل یونیزاسیون (IP) خاصیت آنتی اکسیدانی این نوع از ترکیبات محاسبه شد. یافتهها: با مقایسه میزان BDE و IP ترکیبات شناسایی شده مشخص شد کنیفرول الکل بیشترین و بنزوئیک اسید کمترین خاصیت آنتیاکسیدانی را در دو نمونه شکر پخت (II) و شکر پخت (III) دارا است. نتیجهگیری: استفاده از روش های محاسباتی به منظور تعیین میزان ترکیبات فنولی به خوبی می تواند کارآمد باشد. تفاصيل المقالة -
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12 - Screening Method for Mononitrotoluenes in Natural Waters Using Magnetic Solvent Bar Liquid-Phase Micro-extraction Followed by Gas Chromatography-Flame Ionization Detection
Hadi Farahani Behrooz MirzaA simple andefficient hollow fiber-based method,viz magnetic solvent bar liquid-phasemicroextraction (MSB-LPME) combined with gas chromatography-flame ionization detection (GCFID)has been successfully developed for the trace determination of mononitrotoluenes (MNTs) inn أکثرA simple andefficient hollow fiber-based method,viz magnetic solvent bar liquid-phasemicroextraction (MSB-LPME) combined with gas chromatography-flame ionization detection (GCFID)has been successfully developed for the trace determination of mononitrotoluenes (MNTs) innatural water samples. The analytes were extracted from sample solution to the organic solventimmobilized in a fiber. Following the extraction, the analyte-adsorbed magnetic solvent bar can beeasily isolated from the sample solution by a magnet which could significantlyfacilitate theoperation as well asreducing the total pretreatment time. The bar was mainly eluted withacetonitrile, evaporated to dryness while the residue was dissolved in toluene and finally injectedinto GC-FID. At first, a series of parameters influencing microextraction performance weresystematically investigated and optimized. The values of the detection limit were in the range of0.05-0.08 μg L-1 and the RSD% for the analysis of 50.0μg L-1 of the analytes was below than 5.8%(n = 6). An acceptable linearity (0.996 ≥ r2 ≥ 0.995) and a broad linear range (0.2-200 μg L-1) wereachieved. The method was eventually employed for the preconcentration and determination of theMNTs in environmental water samples and acceptable results were reached. تفاصيل المقالة -
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13 - Change of the tautomeric preference for radical cation of pyruvic acid. DFT studies in the gas phase
Ewa Daniela Raczyńska Malgorzta Hallmann Kinga DuczmalKeto-enol tautomerism was investigated for ionized pyruvic acid using the DFT(B3LYP) method and the larger basis sets [6-31++G(d,p), 6-311++G(3df, 3pd) and aug-cc-pVDZ]. Change of the tautomeric preference was observed when going from the neutral to ionized tautomeric m أکثرKeto-enol tautomerism was investigated for ionized pyruvic acid using the DFT(B3LYP) method and the larger basis sets [6-31++G(d,p), 6-311++G(3df, 3pd) and aug-cc-pVDZ]. Change of the tautomeric preference was observed when going from the neutral to ionized tautomeric mixture. Ionization favors the enolization process (ketoenol) of pyruvic acid, whereas the ketonization (ketoenol) is preferred for the neutral system. Ionization influences also -electron delocalization, which increases exceptionally in the enol form, and slightly decreases in the keto form. تفاصيل المقالة -
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14 - Tautomeric equilibria for ionized oxamic acid - inhibitor of LDH
Ewa D. Raczyńska Małgorzata Hallmann Kinga DuczmalAmide-iminol tautomerism was studied for ionized oxamic acid (OA+•) in the gas phase using theDFT method with the UB3LYP functional and various basis sets {6-31++G(d,p), 6-311+G(d,p), and augcc-pVDZ}. Among twenty tautomers-rotamers possible for OA+•, eleven i أکثرAmide-iminol tautomerism was studied for ionized oxamic acid (OA+•) in the gas phase using theDFT method with the UB3LYP functional and various basis sets {6-31++G(d,p), 6-311+G(d,p), and augcc-pVDZ}. Among twenty tautomers-rotamers possible for OA+•, eleven isomers were found to bethermodynamically stable. Similarly as for the neutral molecule, ionization (OA → OA+• + e) favors theamidization process (amide ← iminol). Isomerization seems to change solely the conformationalpreferences. π-Electron delocalization in the NCO and OCO moieties is close to that for n-π conjugatedfragments. تفاصيل المقالة -
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15 - Magnetic Solvent Bar Liquid-Phase Microextraction Followed by Gas Chromatography-Flame Ionization Detection for the Trace Determination of Selected Polycyclic Aromatic Hydrocarbons in Environmental Water Samples
Hadi Farahani Mohsen ZeebA novel and efficient hollow fiber-based method, viz. magnetic solvent bar liquid-phase microextraction (MSB-LPME) combined with gas chromatography-flame ionization detection (GC-FID) was successfully developed for the trace determination of selected polycyclic aromatic أکثرA novel and efficient hollow fiber-based method, viz. magnetic solvent bar liquid-phase microextraction (MSB-LPME) combined with gas chromatography-flame ionization detection (GC-FID) was successfully developed for the trace determination of selected polycyclic aromatic hydrocarbons (PAHs) in environmental water samples. The target analytes were extracted from sample solution to the organic solvent immobilized in a fiber. After extraction, the analyte-adsorbed magnetic solvent bar could be readily isolated from the sample solution by a magnet which could greatly simplify the operation and also decline the total pretreatment time. The bar was first eluted with methanol, evaporated to dryness while the residue was dissolved in toluene and finally injected into GC-FID. Begin with, effective parameters controlling the performance of the microextraction were evaluated and optimized. The values of the detection limit of the method were in the range of 0.05-0.08 µg L-1 and the RSD% values for the analysis of 10.0 µg L-1 of the analytes was below than 5.8% (n= 6). A good linearity (0.998 ≥ r2 ≥ 0.994) and a broad linear range (0.1-200 µg L-1) were obtained. The method was eventually utilized for the preconcentration and determination of the PAHs in environmental water samples and satisfactory results were obtained. تفاصيل المقالة
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